Measuring Principle; Sensors - TESTO 338 Instruction Manual

3.4.

Measuring principle

3.4.1.

Sensors

1 White LED
2 Light
3 Loaded filter paper
4 Reflected light
5 Optical sensor (photodiode)
Component
Optical sensor
(photodiode and
white LED)
Differential
pressure
sensor/temperatur
e sensor
This sample volume and the measured paper blackening are used
to determine the soot concentration (mg/m³) and also the FSN
(Filter Smoke Number) or the Bosch number.
Process
The white LED radiates light with a defined
intensity on to the blackening mark. The
photodiode calculates the paper blackening
based on the reflected light intensity. The
more soot is deposited on the filter paper,
the less light is reflected.
The sensor for differential pressure
determines the sample volume under
ambient conditions.
The ambient pressure depends on the
height above sea level and weather
(high/low-pressure region). In the case of
the testo 338, the current height above sea
level (with an accuracy of ± 200 m) must be
entered manually. The sample volume
determined by the differential pressure
sensor is used to calculate the sample
volume under reference conditions, with the
input height and the temperature measured
by the instrument.
3 Specifications
11